Absolute quantum heterochromatic photometry of infrared radiation

A description is given of a method for absolute determination of the spectral density of the energy brightness of radiation in the 2–5 μ range. The method does not require the use of a reference standard and is based on three-frequency parametric conversion in a crystal with a quadratic polarizability. The following characteristics of parametric photometers made of lithium niobate, lithium iodate, gadolinium molybdate, and KDP crystals are reported: the spectral dependences of the angles of incidence of the measured radiation, of the directions of propagation of the signal wave, and of the corrections for the absorption and reflection of the radiation in the converter. It is shown that the conversion characteristics optimal for the determination of the brightness in the wavelength range 2–5 μ are exhibited by a gadolinium molybdate crystal.